Seaworthy hydroplanes



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United States Patent O Int. Cl. Bsb 1/20 U.S. Cl, 114-665 17 Claims ABSTRACT F THE DISCLOSURE A hydroplane incorporates a single deltashaped planing surface which generates the major portion of the lift and serves as the basis for the boats ability to navigate in high seas.

BACKGROUND OF THE INVENTION The invention relates to water craft which, when underway, are primarily dynamically borne by a single planing surface. Boats of this kind, employing the planing effect, are known as hydroplanes.

In consequence of buieting received from the waves by the exposed forepart of the planing surface, and because conventional hydroplanes are poorly stable in rough sea, these craft are unseaworthy.

In addition to what is here explained in regard of the state of the art, attention is directed to Ausbau, studyissue for advanced training in the technical fields, De- Cember 1959, pages 798 to 806.

In the design of boats it has been customary to determine the optimum shape from model tests. Based on Froudes law of comparison,

0r Cw-C'a. tan :x4-Cos a The lift-drag ratio Cr sin a Cr Cw e l-Canm'n Vl-Ca. cos a-cos a Ca. cos a Substituting Ca=Ca. sin a gives Ca Cr E COS (2l-zig;

The rst derivative of this function with respect to Ca is l C1` E Ca C'a2 The derivative is zero for C'a =lift gradient, slope of the lift polar curve dCa 1n are measure=-- a=angle of attack.

Ca=lift coeiiicient 3,495,563 Patented Feb. 17, 1970 Using the formula Caopt=\/Ca.Cr .it is possible to compute the optimum lift surface for a given speed and lifting force, provided that the lift gradients of the deltashaped surfaces are experimentally obtained. In most cases, in order to save fuel, the minimum lift-drag ratio is assigned to the service speed.

SUMMARY OF THE INVENTION It is apparent from the formula for CalmI that the optimum lift coefficient depends on the coefficient of friction or on the Reynolds number. This means that the optimum lifting surface, for the same Froude number and lifting gradient and for an increasing Reynolds number, must be larger in a full-scale boat than in a model.

This realization, which is new in model practice, leads to the construction of large, heavy boats having planing surfaces that project outwardly beyond the ships bottoms. Employing this formula enables a saving of one-third in power requirements over modern high-speed boats. In other words, for the same speed and displacement a delta boa (so called because of its characteristic shape) of the invention required only two of the three motors of a conventional high-speed boat, resulting in an appreciable increase in the pay load and reduction in construction costs.

Since previously it was only accidental that a boat had a minimum lift-drag ratio, the invention, which enables designing planing surfaces of optimum size, represents a substantial step forward in boat design.

Likewise, the seaworthiness of the delta boats of the invention, which 'has been substantiated in model tests, is an equally great advance in the art.

Fundamentally, the problem of seaworthiness is solved, in accordance with the invention, by using a planing surface of particular shape, which in the aviation industry is called a delta wing. Its particular advantages are that itS center of pressure is located farther to the rear than is the case with planing surfaces of other shapes, and that changes in the angle of attack shift the center of pressure very little. Because of the advantageous location of the pressure center, the forepart of the delta-shaped planing surface does not have to emerge from the water, provided that the surface is correctly located with respect to the center of gravity of the boat. In this way, the powerful vertical accelerations, caused by the water striking the exposed planing surface, are avoided.

In designing a seaworthy hydroplane it is also necessary to reduce the wave resistance. In conventional hydroplanes the ratio of maximum width at the water line (oating) to length at the Water line (floating) is approximately one-third, whereas this ratio in the delta boats of the invention is approximately one-fifth. As a consequence of the delta boats greater narrowness below the water, the wave resistance declines to one-fourth and decelerations consequently are reduced.

'Ihe third major component of seaworthiness, transverse stability, is automatically solved by using a deltashaped planing surface and by narrowing the shape of the part of the boat that is below the water line.

The novelty of the invention resides in solving the major problems of vertical accelerations, decelerations, and poor transverse stability-which largely constitute the problem of seaworthiness-#by using a delta-shaped planing surface, which covers the ships bottom, and the hydrodynamic effect of which is not closely dependent on the width and length of the hull, as is the case with conventional hydroplanes.

An object of the invention is so to improve the seaworthiness of hydroplanes that they can be used in high seas.

A further object of the invention is the determination of the physical conditions which enable construction of 3 seaworthy hydroplanes having optimum lift-drag ratios at service speeds.

The hydroplanes of the invention, because of their characteristic shape, are called delta boats.

BRIEF DESCRIPTION OF THE DRAWING The invention will be described in detail with reference to the accompanying drawing, wherein:

FIG. la: is a side elevation view of a conventional hydroplane,

FIG. lb is a plan view thereof,

FIG. 1c is a section taken along line c-c in FIG. 1b,

FIG. 1d is a section taken along line d-d in FIG. 1b,

FIG. le is a section taken along line e-e in FIG. lb,

FIG. 2a is a plan view of a hydroplane according to the invention, the planing surface of which is straight and has a positive keel angle,

FIG. 2b is an elevation view thereof,

FIG. 2c is a section taken along line c--c in FIG. 2a,

FIG. 2d is a section taken along line d-a in FIG. 2a,

FIG. 2e is a section taken along line e-e in FIG. 2a,

FIG. 3a is a plan view of a second embodiment according to the invention, the planing surface of which is longitudinally curved and has a positive keel angle,

FIG. 3b is an elevation view thereof,

FIG. 3c is a section taken along line c-c in FIG. 3a,

FIG. 3d is a section taken along line d-d in FIG. 3a,

FIG. 4a is an elevation view of a third embodiment of the invention, the planing surface of which is longitudinally curved and has a negative keel angle.

FIG. 4b is a plan view thereof,

FIG. 4c is a section taken along line c-c in FIG. 4b,

FIG. 4d is a section taken along line d-d in FIG. 4b,

FIG. 4e is a section taken along line e-e in FIG. 4b, and

FIG. 4f is a section taken along line f-f in FIG. 4b.

DESCRIPTION OF THE PREFERRED EMBODI- MENTS OF THE INVENTION FIGS. la-lc show a conventional hydroplane when planing in the water. The abbreviation GWL indicates the water line of the boat when it planes, and RWL the water line when the boat is at rest and floating. The planing surface 1 covers the entire bottom of the boat. The sides of this surface are sharply bounded by the bilge 2 and at the rear by the stern 3. The ratio of maximum width b of the planing surface to its length l is 0.3. The ratio b2/F of the surface 1 ranges from 0.4 to 0.6 depending on degree of immersion, F being the wetted lifted surface. The value of A determines the induced resistance wherein A is the aspect ratio, Ca is the lift gradient, and Cw, is the total resistance.

The shaped (not cross hatched) portion of the planing surface 1 is approximately 50% greater in area than the lifting surface 4. Thus, when a wave crest is struck, the lifting force increases 50%, as a consequence of which the hydroplane shoots out of the water and can, in certain circumstances, rupture from the impact. Moreover, the longitudinal stability is adversely affected, since the center of pressure 5 shifts to 6 nearer the prow.

As seen in FIGS. lc-le, the angle from the keel to the lbilge 2 is positive. The sides 11 of the boat are more radically slanting fore than they are at 12 at midships. When the hydroplane floats, the center of gravity 13 coincides with the center of buoyancy.

FIGS. 2a-2e show a delta boat having a delta-shaped planing surface 17 that is small relative to the peripheral area 16. Although the planing surface juts out beyond the boats bottom 18, it does not extend beyond the maximum width of the boat-an advantage when coming into shore or docking. The side edges 19 of the planing surface 17 lie just above the water line when the boat planes, so

that the additional lifting force is very small, yet is sufiiciently large to ensure that the craft is inherently longi tudinally and transversely stable with respect to small waves. With respect to the boats center of gravity 20, the planing surface 17 is so arranged that its pressure center 21, which, relative to the length of the surface 17, is far aft, is located near the center of gravity 20. This requires a step 22, which lies between the boats center of gravity and the stern 23. The crafts bottom 24 near the stern slopes negatively, so that the spray from the planing surface does not wet it and so that the center of buoyancy shifts fore when the boat floats.

The planing surface has adjustable flaps 25, which, as on delta wings, are located at the step. They serve to increase the value of Ca when the craft lifts from the water, to control the transverse stability when planing, and to improve the maneuverability of the boat when it floats. When floating, the delta boat has a far better liftdrag ratio than conventional hydroplanes, since the turbulence at the stern is far less. When the flaps 25 are in a negative position, the step jump can be avoided. This feature is very important for patrol boats, which plane only when pursuing.

The ratio of boat width to boat length, b/l, is l/6. the delta boat of the invention is much slimmer than conventional hydroplanes. When passing through high waves lifting forces are exerted on the boats sides 26, 27, and 28, which forces are greatly reduced by the large angle made by the sides and render the craft so stable that it can move fast through heaving seas and not capsize. This excellent seaworthiness arises from the fact that the boats sides are built as slanting planing surfaces with a sharp edge 29 and without bending aft. Thus, when the craft rolls, the sides create restoring moments that pass through the crafts center of gravity.

The ratio bZ/F of the planing surface 17 is 0.8. The center line of the surface 17 is straight. The upper face 31 of the planing surface runs parallel to the water line, so that water sweepingover this face causes no downward pressure.

FIGS. Baz-3d show an embodiment of the delta boatwhich has a larger planing surface 36 with respect to the peripheral area 35 than the preceding embodiment.

This indicates a smaller Froude number (VA/gl) for the same displacement. The planing surface is delta shaped and has a bZ/F of 0:6. The center of pressure 38 of the planing surface is, compared to the length of the latter, located even more aft than that of the planing surface 17, since the surface 36 defines a longitudinal arch 39 towards the stern. The longitudinal arching of the planing surface results in increased buoyancy and an improved lift drag ratio, provided that [J2/F exceeds 0.4.

The ratio of boat length to boat width, l/b, is 4.8. The wave resistance is determined by the entrance angle 4S. which is identical with the aft angle formed by the planing surface, and by the length-to-width ratio of the wetted hull-in an actual case, l/b. Since the wave resistance increases as the fourth power of the width of. the midship section, it is essential that the bottom of the craft be kept narrow, in order to prevent marked deceleration when moving through high waves.

This embodiment enables for the rst time the optimum lift-drag ratio and excellent seaworthiness to be combined. To obtain an optimum lift-drag ratio, the lift coefficient C,a=displacement should approach Ca=\/Ca.Cr at service speed. The letter q stands for hydrodynamic pressure and F for the wetted lifting surface. The lift gradient Ca is obtained experimentally and is essentially dependent on the b2/F and on the shape of the planing surface. For delta-shaped planing surfaces for full-size boats the optimum lift coefficient lies between 0.03 and 0.05, or substantially higher than the usual Ca values of modern high-speed craft.

The delta-shaped planing surface 36 can be extended by lateral hydrofoils 40. The inherent transverse stability of the boat is increased when the hydrofoils cut through the water. In order to improve the maneuverability of the boat whenloating, the hydrofoilscan be pivoted against the sides, as shown at 42, by hydraulic cylinders 41.

The boat includes a bow rudder 44 to which is fixed an under-water hydrofoil 43 which acts to control the longitudinal stability, as, for example, when the pay load shifts the center of gravity.

FIGS. 4-4f show a submersible boat having an l/ b exceeding .10 and a b2/F of 0.45. The lift surface is composed of .the fore portion 46 'of the boats bottom, which portion is advantageously negatively keeled, and of a delta @ving 47, the under surface of which lies sufficiently deeply below the water surface 48 so that the submersion affords an inherent transverse stability. The fore part of the boats bottom is longitudinally arched, as shown in dashed lines in FIG. 4a.

A propulsion arrangement 49 is mounted on the end of each delta wing. The high water line 50 shows that the boat is'fheavy for its volume. Therefore, the planing surface mst project considerably beyond the hull in order to obtain the necessary lift with the previously given values for Ca.

The embodiment of FIGS. 4a-4b is actually a combination hydroplane and submersible boat. It does not submerge as conventional submarines do by filling tanks with water,l but instead is held under water by a dynamic downward pressure. The flaps 51 and 52 are used during planing as well as when the boat is' submerged, said aps being hinged for respective pivotal movement Vabout axes X-X and AY-Y in FIG. 4b. When the propulsion stops the boat automatically surfaces.

The planing surface may act as a control means, enabling the craft to plane as well as to move submerged.

I claim:

1. A hydroplane having a bottom surface which is provided with a step therein aft of the center of gravity of the craft, and wherein the ratio of the entire boat length to the maximum boat width at the floating line is greater than 4, an improvement which comprises means on the bottom of the hydroplane defining a single delta-shaped planing surface which generates the major portion of lift for the boat, said surface having a ratio b2/Fb which is not less than 0.4 with complete wetting and remains substantially constant at all speeds, whereby both the liftdrag ratio and the seaworthiness of the craft are improved, b representing the width of the delta-shape planing surface, and Fb the wetted lifting surface thereof, said planing surface being wider than the bottom of the boat at the aft thereof, whereby wave resistance in high seas is reduced.

2. The hydroplane as defined in claim 1, wherein said planing surface is so dimensioned that at the crafts serv ice speed the lift coefficient Ca equals '\/Ca.Cr.

3. The hydroplane as defined in claim 1, wherein the boats sides are built as stabilizing planing surfaces which, when the craft rolls, create restoring moments that pass over the crafts center of gravity.

4. The hydroplane as defined in claim 1, including fiaps located on said planing surface near the step for accelerating the transition from floating to planing and for controlling the traverse stability.

5. The hydroplane as defined in claim 1, including pivotal lateral hydrofoils located on the sides of the craft for increasing the lift coefficient Ca at low speeds and the transverse stability thereof.

6. The hydroplane as defined in claim 5, wherein said hydrofoils constitute extensions of said planing surface when they are pivoted into the plane thereof.

7. The hydroplane as defined in claim 6, including means for pivoting said hydrofoils against the sides of the craft and out of use.

8. The hydroplane as defined in claim 1, wherein said planing surface is curved.

9. The hydroplane as defined in claim 8, wherein said planing surface is curved longitudinally.

10. The hydroplane as defined in claim 9, wherein said planing surface is arched in its aft portion.

11. The hydroplane as defined in claim 8, wherein said planing surface is curved transversely thereof.

12. The hydroplane as defined in claim 11, wherein said planing surface is transversely curved in its aft portion.

13. The hydroplane as defined in claim 1, wherein said planing surface generates a downward force, whereby the craft can plane as well as move submerged.

14. The hydroplane as defined in claim 13, wherein said planing surface acts as a control means, whereby the craft can plane as well as move submerged.

15. The hydroplane as defined in claim 1, including propulsion means, said means defining said planing surface including a delta wing projecting from the two sides of the craft, and said propulsion means being mounted on the end of each projecting portion of said delta wing.

16. The hydroplane as defined in claim 1, including a rudder, and an under-water hydrofoil mounted on said rudder for controlling the longitudinal stability of the craft.

17. Ihe hydroplane as defined in claim 16, wherein said rudder is mounted on the bow.

References Cited UNITED STATES PATENTS 1,413,383 4/1922 Besson 114-66.5 3,225,729 12/ 1965 Ewing 114-665 3,23 0,920 l/ 1966 PiskorZ-Nalecki 114-162 3,343,513 9/1967 Bader 114-665 FOREIGN PATENTS 506,836 =6/1920 France.

ANDREW H. FARRELL, Primary Examiner 

